High-Intensity Focused Ultrasound (HIFU) phased arrays allow flexibility in beam steering, beam shaping, and dynamic focusing. These features enable them to create large and contiguous tissue lesions of predetermined shape with high efficiency, resulting in shorter treatments, increased accuracy, and ease of operation. The goal of this proposal is to replace the current Sonablate HIFU transducers (mechanically scanned, dual-element, HIFU and imaging capability) used in the clinic for the treatment of BPH and localized prostate cancer with a 2-D HIFU phased array. The array will eliminate "probe switching" during treatment, reduce the reliance on mechanical scanning, and increase treatment effectiveness through dynamic focusing and focal zone shaping. During Phase I, phased array configurations were simulated to determine an optimum design for HIFU prostate treatments. A 1-D truncated spherical annular array and electronics were fabricated and characterized. In this Phase II application, we propose to build on these encouraging results by: 1) defining and optimizing a HIFU phased array with 2-D focusing capability, 2) fabricating and characterizing the array, 3) integrating it into a transrectal image-guided HIFU probe to be used with the Sonablate system, and 4) evaluating its performance in-vitro and in-vivo using a canine prostate model. PROPOSED COMMERCIAL APPLICATION: As our population ages, prostate disease (BPH & cancer) is becoming an ever-more-frequent malady for man. The annual market for treatment of prostate cancer in the U.S. is estimated around $5 billion. Focus Surgery Inc. manufactures the Sonablate(TM) system, which makes use of HIFU technology to treat benign prostatic hyperplasia (BPH). To extend the application of this system to treat localized prostate cancer increased flexibility in focal spot placement and less reliance on mechanical steering is required. The current proposal directly addresses this challenge. Successful completion of this project will open the enormous market of prostate cancer treatment to our Sonablate(TM) device.